In many printing systems, such as inkjet printing systems, sheets of print medium to be printed are conveyed or transported by belt-type conveyor mechanisms. For example, such a belt-type conveyor mechanism will typically convey or transport the sheets to be printed into and through an image forming device or printing head of the printing system. To achieve high print quality in an inkjet printing system, the distance between the printing heads and the sheet to be printed is desirably kept small. Furthermore, to obtain optimum performance and output quality in a printing system, particularly an inkjet printing system, it is important to control the position of the sheets with respect to the printing heads of the image forming device very accurately. In this regard, an inkjet printing system aims to achieve micrometer accuracy in the positioning of ink droplets from the inkjet print heads operating at a fixed frequency.
It has been found that manufacturing tolerances and operating variations generally make it too difficult to provide a belt-type conveyor mechanism which operates at a sufficiently precise velocity and/or a reliably repeatable velocity for the level of accuracy desired in delivery of print medium sheets to an image forming device or to the printing heads in an inkjet printing system. To address this issue, a system has been developed which synchronizes operation of the image forming device or the printing heads with the movement of the conveyor mechanism. Accordingly, in developments to date, a system for operating the image forming device or inkjet printing heads based on movement of the conveyor drive mechanism has been proposed. This way, a precisely known constant speed or velocity of the conveyor mechanism should no longer be of primary relevance for accurate positioning of the ink droplets from the inkjet print heads. It has been found, however, that such a system still produces discrepancies or mismatches between the actual and the desired ink application.
US 2009/196662 A relates to a method of ensuring a correct lateral registration setting, in a digital multi-color electrographic sheet-printing machine, in which the sheets adhere to a support, preferably a transport belt, are transported past printing units.